[Python-ideas] discontinue iterable strings

[Michael Selik]

On Sun, Aug 21, 2016 at 2:46 AM eryk sun <eryksun at gmail.com> wrote:

> On Sun, Aug 21, 2016 at 6:34 AM, Michael Selik <michael.selik at gmail.com>
> wrote:
> > The detection of not hashable via __hash__ set to None was necessary, but
> > not desirable. Better to have never defined the method/attribute in the
> > first place. Since __iter__ isn't present on ``object``, we're free to
> use
> > the better technique of not defining __iter__ rather than defining it as
> > None, NotImplemented, etc. This is superior, because we don't want
> __iter__
> > to show up in a dir(), help(), or other tools.
>
> The point is to be able to define __getitem__ without falling back on
> the sequence iterator.
>
> I wasn't aware of the recent commit that allows anti-registration of
> __iter__. This is perfect:
>
>     >>> class C:
>     ...     __iter__ = None
>     ...     def __getitem__(self, index): return 42
>     ...
>    >>> iter(C())
>     Traceback (most recent call last):
>       File "<stdin>", line 1, in <module>
>     TypeError: 'C' object is not iterable
>     >>> isinstance(C(), collections.abc.Iterable)
>     False
>

For that to make sense, Iterable should be a parent of C, or C should be a
subclass of something registered as an Iterable. Otherwise it'd be creating
a general recommendation to say ``__iter__ = None`` on every non-Iterable
class, which would be silly.
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